Calcium-induced inhibition of taurine transport in brush-border membrane vesicles from rabbit small intestine

The influence of Ca²⁺ on the activity of the taurine transport system was investigated in rabbit small intestinal brush-border membrane vesicles. Preincubation of the brush-border membrane vesicles with Ca²⁺ prepared by the Mg²⁺-aggregation method markedly decreased the NaCl gradient-dependent uptake of taurine in these vesicles. Uptake of glucose and alanine, both dependent on a Na⁺ gradient, were also decreased by Ca²⁺-treatment, but their reduction was very small compared with that of taurine uptake. The inhibitory effect of Ca²⁺ was dose- and time-dependent. The inhibition was reduced by the presence of ethylene glycol-bis(β-amino ethyl ether)-N,N,N′-N′-tetraacetic acid during treatment of the membrane vesicles with Ca²⁺. Neomycin partially protected the taurine transporter activity from the Ca²⁺-induced inhibition, but indomethacin did not. 5-Nitro-2-(3-phenylpropylamino)benzoate, a Cl^--channel blocker, did not increase taurine uptake in the Ca²⁺-treated membrane vesicles. It is concluded that the Ca²⁺-induced inhibition of taurine uptake in rabbit intestinal brush-border membrane vesicles is not due to accelerated dissipation of the ion gradient driving forces across the membrane but rather to a direct effect on the transporter, most likely mediated by the activation of the membrane-bound phospholipase C.